Known photoresist materials, including chemically amplified photoresists (CAR) face many challenges for application in Extreme Ultraviolet (EUV) lithography. To achieve higher resolution and/or lower line-edge and line-width roughness (LER/LWR), the CAR materials demands entail a high EUV dose, which high dose may be uneconomical given the high cost of EUV power. For example, up to 96% of EUV power is lost in optics of an EUV system before EUV radiation reaches a substrate to be exposed. In the last few years, alternative photoresist systems such as metal-oxide photoresist and metal-containing photoresist have been explored. Advantages provided by such alternative photoresist systems include increased absorption of incident EUV photons as well as better etch selectivity, allowing thinner photoresist layers to be used for patterning of a substrate.
There are also several limitations for the use of known metal-oxide or metal-based photoresist architecture. One limitation is the finite lifetime of photoresist materials that incorporate metal-oxide nanoparticles into a photoresist matrix. In order to provide acceptable shelf life these photoresist materials may employ a stabilizer to stabilize a nanoparticle suspension, adding to cost and reducing sensitivity of the photoresist material.
Moreover, dispensing and maintaining an acceptable degree of uniformity of nanoparticle suspension within a photoresist at the nanometer length scale may be particularly challenging. Many of the sensitizers that may be used in a photoresist formulation also readily sublime during a soft bake operation, resulting in additional non-uniformity. This inhomogeneity may lead to difficulty in controlling LWR, as well as difficulty in controlling critical dimension (CD).
Because metal-based photoresists are highly etch-resistant, metal-based photoresists may be applied as thinner layers for patterning a substrate than conventional CAR materials, as thin as ˜15 nm, for example. The thinner film imparts the advantage of being less susceptible to pattern collapsing, but also entails a smaller photoresist volume and thus less photons being absorbed. Accordingly, more noise and worse LER/LWR may result from such thin photoresists. Increasing the film thickness, runs the risk of generating a patterned photoresist feature having a “T-topping” structure, where the photoresist feature may exhibit a “T” shape in cross-section after patterning and development. That is, the photon availability attenuates as a function of thickness of the photoresist, due to strong absorption by the metal sensitizers. Because of greater photon density at the top of a photoresist feature, and since most existing metal-based photoresists are negative tones, this photon attenuation results in a photoresist profile resembling a “T” or a reversed pyramid. While negative tone photoresists in general are better for improving small pitch resolution this advantage is offset by the T-topping problem.
Another issue with the employment of photoresist containing metal oxide particles or metal particles is that metal hydrides may form in a scanner of a EUV lithographic tool due to reaction between the photoresist and hydrogen used in the scanner. The metal hydrides may deposit on the EUV mirror surfaces, reducing optics lifetime.
With respect to these and other considerations, the present embodiments are provided.